Pilot FriXion Colors Erasable Marker - 12 Color Set
These are the most amazing pens I've encountered. I like to draw in pen, namely because it looks sharper, and erasable pens usually suck. BUT these erase with friction (both in gel and marker pen style), leaving NO trace, and no eraser shavings. It erases better than pencils and doesn't smudge during use. I'm smitten.